Systems and methods for controlling gas powered appliances

ABSTRACT

A control system for a gas powered appliance includes a power source to provide electrical power to control at least one electrically actuated gas valve, a valve control system to selectively couple electrical power from the power source to the electrically actuated gas valve, and a controller. The valve control system includes a first switch and a second switch. The first switch and the second switch are electrically connected in series between the power source and the electrically actuated gas valve. The controller is operatively connected to the first switch and the second switch and configured to control the first switch and the second switch to selectively couple power from the power source to the electrically actuated gas valve.

FIELD

The field of the disclosure relates generally to gas powered appliances,and more particularly, to systems and methods for controlling operationof a gas powered water heater.

BACKGROUND

Storage water heaters may be utilized domestically and industrially invarious applications. Domestically, a storage water heater is used forgeneration of hot water that may be used for bathing, cleaning, cooking,space heating, and the like.

A conventional gas fired water heater includes a water storage tank andgas fired burner assembly for heating water within the tank. Inoperation, combustion gases generated by the firing of the burnerassembly may be directed upwardly through a flue pipe via a hood. Thecombustion gases serve to transfer heat to the water contained withinthe storage tank. The top of the water heater may include suitablefittings for connection to a supply of water and a water distributionsystem with a water inlet provided with a dip tube, which serves todirect the inflow of cold water to the bottom of the tank.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

SUMMARY

In one aspect, a control system for controlling a gas powered applianceincluding at least one electrically actuated gas valve for selectivelyproviding gas to a burner is described. The control system includes apower source to provide electrical power to control the at least oneelectrically actuated gas valve, a valve control system configured toselectively couple electrical power from the power source to theelectrically actuated gas valve, and a controller. The valve controlsystem includes a first switch having an on state to permit current topass through the first switch and an off state to prevent current frompassing through the first switch, and a second switch having an on stateto permit current to pass through the second switch and an off state toprevent current from passing through the second switch, the first switchand the second switch electrically connected in series between the powersource and the electrically actuated gas valve. The controller isoperatively connected to the first switch and the second switch andconfigured to control the first switch and the second switch toselectively couple power from the power source to the electricallyactuated gas valve.

In another aspect, a water heater includes a storage tank, a main burnerconfigured to burn gas to heat water in the storage tank, a main gasvalve, and a control system configured to control operation of the mainburner to provide water in the storage tank substantially at a setpointtemperature. The main gas valve is coupled to the main burner and has anopen position permitting gas flow through the main gas valve and aclosed position preventing gas flow through the main gas valve. The maingas valve is an electrically actuate gas valve. The control systemincludes a power source to provide electrical power, a valve controlsystem configured to selectively couple electrical power from the powersource to the main gas valve, and a controller. The valve control systemincludes a first switch having an on state to permit current to passthrough the first switch and an off state to prevent current frompassing through the first switch, and a second switch having an on stateto permit current to pass through the second switch and an off state toprevent current from passing through the second switch, the first switchand the second switch electrically connected in series between the powersource and the main gas valve. The controller is operatively connectedto the first switch and the second switch and configured to control thefirst switch and the second switch to selectively couple power from thepower source to the main gas valve.

Various refinements exist of the features noted in relation to theabove-mentioned aspects. Further features may also be incorporated inthe above-mentioned aspects as well. These refinements and additionalfeatures may exist individually or in any combination. For instance,various features discussed below in relation to any of the illustratedembodiments may be incorporated into any of the above-described aspects,alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away view of a water heater including one embodiment ofa control system for controlling operation of the water heater.

FIG. 2 is a block diagram of a computing device for use in the waterheater shown in FIG. 1.

FIG. 3 is a schematic block diagram of the control system shown in FIG.1.

FIG. 4 is a schematic block diagram block of an embodiment of thecontrol system shown in FIG. 3.

FIGS. 5A-5D is a circuit diagram of an embodiment of the control systemshown in FIG. 3.

FIG. 6 is a circuit diagram of part of a valve control system for use inthe control system shown in FIGS. 5A-5D.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The embodiments described herein generally relate to water heaters. Morespecifically, embodiments described herein relate to methods and systemsfor controlling operation of a gas powered water heater.

Referring initially to FIG. 1, a control system 100 is provided forcontrolling operation of a water heater 20 to maintain a desiredtemperature of water in the water heater 20. The water heater 20 has astorage tank 22 that stores heated water and receives cold water via acold water inlet 26. Cold water entering a bottom portion 28 of thestorage tank 22 is heated by a fuel-fired main burner 30 beneath thestorage tank 22. Water leaves the storage tank 22 via a hot water outletpipe 34. Combustion gases from the main burner 30 leave the water heater20 via a flue 36. The control system 100 provides for control of gasflow via a gas supply line 40 and one or more valves (not shown) to themain burner 30, as described herein. The gas burned by the water heater20 may be natural gas, liquid propane (LP) gas, or any other suitablegas for powering a water heater. Moreover, the control system 100controls a standing (i.e., continuously lit) pilot burner 41 thatoperates as an ignition source for the main burner 30. The controlsystem 100 also controls gas flow via gas line 40 and one or more valves(not shown in FIG. 1) to the pilot burner 41. Alternatively, theignition source may be a piezoelectric lighter or any other suitableignition source. In some embodiments, a piezoelectric lighter is used toignite the pilot burner 41.

The control system 100 includes a sensor 102 that provides an output orvalue that is indicative of a sensed temperature of the water inside ofthe storage tank 22. For example, the sensor 102 may be a tanksurface-mounted temperature sensor, such as a thermistor. Alternatively,in other embodiments, the sensor 102 may be a temperature probe or anyother sensor suitable for measuring the water temperature in storagetank 22. In the embodiment shown in FIG. 1, sensor 102 is positionedproximate bottom portion 28 of the storage tank 22. Alternatively, thesensor 102 may be positioned to detect the temperature of the water inthe storage tank 22 at any other suitable portion or portions of thestorage tank, such as a middle portion 31, an upper portion 32, or acombination of bottom, middle, and/or upper portions. Moreover, thecontrol system 100 may include more than one sensor 102. For example,the control system 100 may include two or more temperature sensors 102for detecting the water temperature at one or more locations in thestorage tank 22. In one example, the control system 100 include twosensors 102 that are thermistors mounted on a circuit board positionedwithin a watertight tube near the bottom of the storage tank 22. The twothermistors detect the temperature of the water near the bottom portion28 of the storage tank 22.

The control system 100 is positioned, for example, adjacent the storagetank 22. Alternatively, the control system 100 is located underneath thestorage tank 22, in a watertight compartment within the storage tank 22,or in any other suitable location. Sensor 102 is in communication withcontrol system 100, and provides control system 100 an output or valueindicative of the water temperature in storage tank 22. In someembodiments, a second sensor (not shown) may be disposed at an upperportion 32 of the water heater 20, to provide an output or value that isindicative of a sensed temperature of the water in upper portion 32 ofstorage tank 22.

Various embodiments of the control system 100 may include and/or beembodied in a computing device. The computing device may include, ageneral purpose central processing unit (CPU), a microcontroller, areduced instruction set computer (RISC) processor, an applicationspecific integrated circuit (ASIC), a programmable logic circuit (PLC),and/or any other circuit or processor capable of executing the functionsdescribed herein. The methods described herein may be encoded asexecutable instructions embodied in a computer-readable mediumincluding, without limitation, a storage device and/or a memory device.Such instructions, when executed by a processor, cause the processor toperform at least a portion of the methods described herein.

FIG. 2 is an example configuration of a computing device 200 for use inthe control system 100. The computing device 200 includes a processor202, a memory area 204, a media output component 206, an input device210, and communications interfaces 212. Other embodiments includedifferent components, additional components, and/or do not include allcomponents shown in FIG. 2.

The processor 202 is configured for executing instructions. In someembodiments, executable instructions are stored in the memory area 204.The processor 202 may include one or more processing units (e.g., in amulti-core configuration). The memory area 204 is any device allowinginformation such as executable instructions and/or other data to bestored and retrieved. The memory area 204 may include one or morecomputer-readable media.

The media output component 206 is configured for presenting informationto user 208. The media output component 206 is any component capable ofconveying information to the user 208. In some embodiments, the mediaoutput component 206 includes an output adapter such as a video adapterand/or an audio adapter. The output adapter is operatively coupled tothe processor 202 and operatively coupleable to an output device such asa display device (e.g., a liquid crystal display (LCD), organic lightemitting diode (OLED) display, cathode ray tube (CRT), or “electronicink” display) or an audio output device (e.g., a speaker or headphones).

The computing device 200 includes, or is coupled to, the input device210 for receiving input from the user 208. The input device is anydevice that permits the computing device 200 to receive analog and/ordigital commands, instructions, or other inputs from the user 208,including visual, audio, touch, button presses, stylus taps, etc. Theinput device 210 may include, for example, a variable resistor, an inputdial, a keyboard/keypad, a pointing device, a mouse, a stylus, a touchsensitive panel (e.g., a touch pad or a touch screen), a gyroscope, anaccelerometer, a position detector, or an audio input device. A singlecomponent such as a touch screen may function as both an output deviceof the media output component 206 and the input device 210.

The communication interfaces 212 enable the computing device 200 tocommunicate with remote devices and systems, such as sensors, valvecontrol systems, safety systems, remote computing devices, and the like.The communication interfaces 212 may be wired or wireless communicationsinterfaces that permit the computing device to communicate with theremote devices and systems directly or via a network. Wirelesscommunication interfaces 212 may include a radio frequency (RF)transceiver, a Bluetooth® adapter, a Wi-Fi transceiver, a ZigBee®transceiver, a near field communication (NFC) transceiver, an infrared(IR) transceiver, and/or any other device and communication protocol forwireless communication. (Bluetooth is a registered trademark ofBluetooth Special Interest Group of Kirkland, Wash.; ZigBee is aregistered trademark of the ZigBee Alliance of San Ramon, Calif.) Wiredcommunication interfaces 212 may use any suitable wired communicationprotocol for direct communication including, without limitation, USB,RS232, I2C, SPI, analog, and proprietary I/O protocols. Moreover, insome embodiments, the wired communication interfaces 212 include a wirednetwork adapter allowing the computing device to be coupled to anetwork, such as the Internet, a local area network (LAN), a wide areanetwork (WAN), a mesh network, and/or any other network to communicatewith remote devices and systems via the network.

The memory area 204 stores computer-readable instructions for control ofthe water heater 20 as described herein. In some embodiments, the memoryarea stores computer-readable instructions for providing a userinterface to the user 208 via media output component 206 and, receivingand processing input from input device 210. The memory area 204includes, but is not limited to, random access memory (RAM) such asdynamic RAM (DRAM) or static RAM (SRAM), read-only memory (ROM),erasable programmable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), and non-volatile RAM (NVRAM).The above memory types are example only, and are thus not limiting as tothe types of memory usable for storage of a computer program.

A functional block diagram of the control system 100 is shown in FIG. 3.The control system includes a safety system 302, a power system 304, acontroller 306, sensors 102, a valve control system 308, and a valvepicking system 310. The control system is coupled to and controls afirst valve 314 and a second valve 312. The second valve 312 and thefirst valve 314 are solenoid actuated gas valves for selectivelycoupling gas to the main burner 30 and the pilot burner 41,respectively. An electrical current through the coil of the valve 312 or314 causes the valve 312 or 314 to open. As shown in FIG. 4, gas flowsfrom a gas source to first valve 314. Gas the passes through the firstvalve 314 is provided to the pilot burner 41 and the second valve 312.Gas passing through the second valve 312 is provided to the main burner30.

With reference again to FIG. 3, the power system 304 provides power tothe other components of the control system 100. Specifically, the powersystem 304 provides power to the controller 306 and the valve controlsystem 308. The power system 304 provides an output to the valve controlsystem 308 at a first voltage that is lower than a second voltage outputto the controller 306. The power system 304 may include and/or receivepower from any suitable alternating current (AC) or direct current (DC)power source, such as one or more batteries, thermoelectric generators,photovoltaic cells, AC utilities, and the like. In an exemplaryembodiment, the power system includes an unregulated DC power source(not shown in FIG. 3) with a source resistance between about two andfive ohms. In some embodiments, the unregulated DC power source is athermoelectric generator in thermal communication with the pilot burner41. The thermoelectric generator can be ideally represented by a 650-850mV Thevenin equivalent voltage source with a 2 to 5 ohm Theveninequivalent source resistance.

The safety system 302 is configured to selectively extinguish and/orprevent ignition of the main burner 30 and/or the pilot burner 41.Specifically, the safety system 302, under the direction of thecontroller 306, prevents the power system from providing sufficientvoltage, current, and/or power to hold open the first valve 314 or thesecond valve 312. When the valves 312 and 314 are closed, gas flow tothe main burner 30 and the pilot burner 41 is prevented and ignition ofthe main burner 30 and the pilot burner 41 is thereby prevented. Whenthe controller 306 determines to shut down the water heater 20 using thesafety system 302, the controller 306 outputs a signal to safety system302. In response to the signal, the safety system 302 causes the valves312 and 314 to close (if open) and prevents them from being opened (ifalready closed). In other embodiments, the safety system 302 operates inresponse to a lack of an expected signal from the controller 306. Thus,if the controller does not send (or the safety system 302 otherwise doesnot receive) the expected signal, whether continuously or periodically,the safety system 302 causes the valves 312 and 314 to close.

Responsive to signals from the controller 306, the valve control system308 selectively couples power from the power system 304 to the valves312 and 314 to selectively hold them open. The valve control system 310is responsive to signals from the controller 306 to couple power to oneof the valves 312 or 314 and to signals that instruct it to decouple thevalve 312 or 314 from the power system 304. Moreover, when the valvecontrol system is holding one of the valves 312 or 314 open, the valvecontrol system 308 ceases coupling power to the valves 312 and 314 if itdoes not receive an expected signal from the controller 306. Thus, ifthe controller 306 stops sending the expected signal (or sends anincorrect signal) the valve control system decouples the valve(s) 312and/or 314 from the power system 304, thereby causing the valves 312and/or 314 to close. The expected signal may be a continuous signal, asignal repeated at a particular interval, a signal with a particularduty cycle or frequency, or any other suitable signal.

The valve pick system 310 receives power at the second voltage from thecontroller 306 and opens (also sometimes referred to as “picking” or“picking open”) the main valve 312 when commanded to do so by thecontroller 306. The valve pick system 310 does not open the pilot valve314. The pilot valve 314, in this embodiment, is a manually openedvalve, which may be held open by the valve control system 308 after itis manually opened. Alternatively, the valve pick system 310 may also beoperable to pick the pilot valve 314.

The sensors 102 are temperature sensors operable to provide a signalindicative of the temperature the water in the storage tank 22. Thesensors 102 provide their signals to the controller 306. As describedabove, the sensors 102 are any suitable sensor, such as thermistors,probes, and the like, for detecting the temperature of the water withinthe storage tank. Additionally, or alternatively, the sensors 102 mayinclude any other suitable types of sensors, such as oxygen sensors,ambient air temperature sensors, moisture sensors, etc.

The controller 306 controls operation of the water heater 20 and thecontrol system 100. The controller 306 operates the water heater toprovide water heated to a desired temperature, such as a temperaturesetpoint that is set by a user via the input 210. The controller 306includes a computing device, such as computing device 200. In someembodiments, the controller 306 is a microcontroller. Alternatively, thecontroller 306 includes any combination of digital and/or analogcircuitry that permits the controller 306 to function as describedherein.

In general, the controller 306 controls the water heater 20 based on theinputs from the sensors 102 and the temperature setpoint. Under normaloperations, the controller 306 utilizes the valve control system 308 tohold open the pilot valve 314 to permit gas to flow to the pilot burner41 and the main valve 312 When the water temperature detected by thesensors 102 drops below the a threshold slightly below the temperaturesetpoint, the controller 306 opens the main valve 312 using the valvepick system 310. After the main valve 312 is picked open, the controller306 holds the main valve open by coupling power from the power system304 to the main valve 312 through the valve control system 308. When thecontroller 306 determines, based on the temperature set point and theinput from the temperature sensors 102, to turn off the main burner 30,it decouples the main valve 312 from the power system 304 to close themain valve 312, thereby interrupting the flow of gas to the main burner30 and extinguishing the main burner 30. If an abnormal condition occursat any point during operation, the safety system prevents the powersystem 304 from opening and/or holding open the valves 312 and 314.

FIG. 4 is a block diagram of an example embodiment of the control system100 shown in FIG. 3. FIGS. 5A-5D show a circuit diagram of oneimplementation of the control system 100 shown in FIG. 4. Particularcomponents as shown in FIGS. 5A-5D produce the voltage values andtimings described herein. It should be understood that differentcomponents with the same or different characteristics and/or values maybe used in other implementations.

The power system 304 includes a thermoelectric generator 402, a powerconverter 404, and a voltage switch 406. The thermoelectric generator402 is thermally coupled to the pilot burner 41. The thermoelectricgenerator 402 provides a direct current (DC) electrical output (voltageV1) in response to a flame on the pilot burner 41. Although the outputvoltage V1 will vary based on load, temperature, and other factors,under steady state conditions the voltage V1 will be around 450 mV. Theoutput of the thermoelectric generator 402 is input to the powerconverter 404. The power converter 404 is a modified Colpitts oscillatorthat is self-starting and self-oscillating. The converter 404automatically begins operating in response to the electrical output fromthe thermoelectric generator 402. The power converter 404 produces a DCoutput with a voltage (V2) greater than its input voltage V1. In anexample embodiment, the maximum value of voltage V2 output by theconverter 404 varies between about seventeen times V1 to about ten timesV1 depending on the magnitude of the voltage V1 input to the converter404. In other embodiments, the maximum voltage V2 may have any othersuitable relationship or range of relationships to the voltage V1. Atsteady state, the converter 404 will provide an output voltage ofapproximately 5 volts. When the voltage V2 is coupled to the controller306, the controller 306 turns on and begins controlling operation of thewater heater 20.

The control system 100 includes a flame loss feedback safety feature.The thermoelectric generator's thermal communication with the pilotburner 41 produces the current to hold open the pilot valve 314. If theflame on the pilot burner 41 is lost, the output voltage from thethermoelectric generator 402 will decrease until there is insufficientcurrent to hold open the pilot valve 314. Because gas flows through thepilot valve 314 to the main valve 312 (and the main burner 30), the lossof flame on the pilot burner 41 causes the pilot valve 314 to close andinterrupt gas flow to both the pilot burner 41 and the main burner 30.This may help prevent gas from being delivered to the pilot burner 41 orthe main burner 30 when there is no ignition source available for thegas.

The voltage switch 406 is located between the converter 404 and thecontroller 306. The voltage switch 406 defaults to an OFF(non-conducting) state and turns ON when its supply voltage (i.e., theoutput of converter 404) reaches a first threshold. The voltage switch406 also turns OFF if its supply voltage falls below a second, lowerthreshold. The voltage switch 406 selectively connects the voltage V2 tothe controller 306 to power the controller 306. At startup, thethermoelectric generator 402 output V1 will be zero and it will ramptoward its steady value over several minutes. When voltage V1 reachesapproximately 50-100 mV, the power converter 404 will turn on and itsoutput voltage V2 will begin ramping toward its steady state value of5V. The ramp to 5V can take 30-60 seconds depending on the V1 ramp rate.When the converter 404 output voltage V2 reaches the first threshold,the voltage switch 406 turns ON and the power supply voltage of thecontroller 306 will immediately rise to a voltage substantially equal tothe first threshold. The voltage output from the voltage switch 406 willbe slightly less than the voltage V2 because there is a small voltagedrop across the voltage switch 406. The voltage drop depends on theparticular device used for the voltage switch 406 and the ambienttemperature. In an example embodiment, the voltage drop is between about0.1 volts and 0.2 volts. This provides a “hard-edge” to the controller306 power supply pin and other systems that use the controller 306 powersupply voltage. The voltage switch 406 also provides a reference forsoftware timings as the software can assume the supply voltage of thecontroller 306 is roughly equal to the first threshold at the start ofcode execution. The voltage switch 406 includes hysteresis so that itwill not turn OFF if the voltage V2 falls back below the first thresholdvalue. The OFF threshold for the voltage switch 406 is set to a second,lower threshold value that is below the brown-out voltage for thecontroller 306. In the example embodiment, the first threshold value isabout 3.5 volts, the brownout voltage of the controller 306 is about 1.8volts, and the second threshold value is less than 1 volt. If V2 dropsbelow 1.8V, the controller 306 will brown-out before the voltage switch406 turns off. Alternatively, the second threshold may be a value thatis not below the brown-out voltage of the controller 306. For example,the second threshold voltage may be set at 2.5V. The voltage V2 couldthen vary between 5 volts and 2.5 volts without the voltage switch 406turning off. Because the second threshold is above the brownout voltage,the voltage switch 406 will be turned off by a decreasing voltage V2before the brownout voltage of the controller 306 is reached.

The safety system 302 includes a safety switch control circuit 408 and asafety switch 410. In the illustrated embodiment, the safety switchcontrol circuit 408 is coupled to the output of the voltage switch 406,the safety switch 410, and a control pin of the controller 306. Thesafety switch 410 is also coupled between the output of thethermoelectric generator 402 and ground. In the example embodiment, atstartup, the pin of the controller 306 that is coupled to the safetyswitch control circuit 408 is held in a high impedance (Hi-Z) state. Thesafety switch control circuit 408 includes a timing circuit, e.g., an RCcircuit defining an RC time constant, that is enabled by placing thecontroller 306 pin in the Hi-Z state. When the voltage switch 406 turnson, the safety switch control circuit 408 will slowly charge toward thevoltage V2. If the voltage of the safety switch control circuit 408reaches a threshold value, the safety switch control voltage will causethe safety switch 410 to turn on. When the safety switch 410 is turnedon, the thermoelectric generator output is substantially shorted toground and there is insufficient power available to hold open the mainvalve 312, hold open the pilot valve 314, operate the converter 404, andoperate the controller 306. If the pin of the controller 306 that iscoupled to the safety switch control circuit 408 is switched to alogical low state before the safety switch control circuit 408 reachesthe threshold value, the timing circuit is disabled and the safetyswitch 410 does not turn on. Alternatively, the safety switch controlcircuit 408 may not be coupled to the voltage switch 406 and the pin ofthe controller 306 that is coupled to the safety switch control circuit408 is not held in a Hi-Z state at startup. In such embodiments, the pinof the controller 306 coupled to the safety switch control circuit 408is driven high or low to turn the safety switch 410 on or off.

The thermoelectric generator 402 is an unregulated DC power source thatcan be represented by a 650 mV to 850 mV Thevenin equivalent voltagesource with a 2 to 5 ohm source resistance at optimal steady state. TheThevenin equivalent voltage generally decreases as ambient temperaturearound the generator 402 increases, such as after the main burner 30 hasbeen on for a long time. Because of the thermoelectric generator 402power supply characteristics, the size of its load (in ohms) willdetermine the voltage over the load. Substantially lowering the overallload on the thermoelectric generator 402, by switching in a parallel lowresistance load (e.g., resistor 506 shown in FIG. 5D) or shortingdirectly to ground (e.g., resistor 506 is substantially 0 ohms) via thesafety switch 410, substantially lowers the voltage (V1) because of thevoltage divider created with the source resistance and the new loweroverall load. The safety switch 410 load is sized so that when it isswitched on it will lower the voltage V1 below the voltage required tohold open the valves 312 and 314 and below the voltage required to startthe converter 404. Moreover, the size of the safety switch load (and itspresence or absence) is determined according to the source impedance ofthe power source. If the source impedance of the power source isrelatively low, the safety switch load should be greater than 0 ohms tolimit the current and drop the output voltage substantially across thesafety switch load. In the example embodiment, the safety switch 410load is sized to drop the load resistance to about 0.24 ohms and thevoltage V1 drops to about 40 mV. Alternatively, because thethermoelectric generator 402 has a relatively high source impedance, thesafety switch 410 couples the output of the thermoelectric generator 402directly to ground without inclusion of a parallel low resistance load.In one example, the safety switch 410 load is sized to drop the loadresistance to about 0 ohms and the voltage V1 to between about 10 mV andabout 15 mV.

In normal startup operation, the controller 306 will change the outputof its safety switch control pin to a low state within a preset amountof time, preventing the voltage of the safety switch control circuit 408from reaching the threshold to turn on the safety switch 410. Thecontroller 306 changes the output of the safety switch pin to a lowstate after the controller 306 passes all internal microprocessor andhardware checks (internal microprocessor checks can take from 4 to 6seconds after the voltage switch 406 turns on and the controller 306begins executing instructions). In embodiments in which the safetyswitch control circuit 408 is not coupled to the voltage switch 406, thesafety switch control pin begins in the low state during normal startupoperations. During normal operation of the water heater 20, thecontroller 306 will maintain the output pin coupled to the safety switchcontrol circuit 408 in a low state, thus keeping the voltage of thesafety switch control circuit 408 from reaching the threshold to turn onthe safety switch 410. If the controller 306 determines to shut thevalves 312 and 314 of the water heater 20 for safety reasons, thecontroller 306 switches the safety circuit output pin to a high state.When the output pin is high, the safety switch circuit 408 charges tothe threshold to turn on the safety switch 410 at a rate that is fasterthan the rate when the pin is in the Hi-Z state.

In some embodiments, the controller also sets the safety switch enablepin to a high impedance state (thus allowing the safety switch controlvoltage to charge) before providing signals to hold open the valves 312and 314. The safety switch enable pin is then driven low once thesignals are completed. In this way if the controller 306 malfunctionsand becomes stuck in the state when signaling to the valves is ON, thesafety switch 410 will eventually charge and shut the system down.

The valve control system 308 includes a first main switch 412, a secondmain switch 414, a main charge pump 416, a pilot switch 418, and a pilotcharge pump 420. As described above, the controller 306 selectivelyholds open the main valve 312 and the pilot valve 314 via the valvecontrol system 308, which may also be referred to as a valve holdingsystem. The controller 306 holds the pilot valve 314 open by closing thepilot hold switch 418 to couple the pilot valve 314 to thethermoelectric generator 402 output. Specifically, the controller 306supplies periodic bursts of pulse width modulated (PWM) signals to thepilot charge pump 420. The PWM signals are square waves with anamplitude that switches from 0 volts to substantially the voltage V2.The burst of PWM signals charge the pilot charge pump 420 to a voltageV3 sufficient to turn on the pilot switch 418. In the exemplaryembodiment, the voltage V3 is less than the voltage V2. The magnitude ofthe voltage V3 will vary with the varying of voltages V1 and V2. Whenthe voltage V2 is about 5 volts, the exemplary voltage V3 will be about3 volts. In other embodiments, the voltage V3 may be the same as orgreater than the voltage V2 depending on the voltage needed to turn onthe pilot switch 418. In one embodiment, V3 is about 3.25 volts. Thecontroller 306 periodically provides PWM signal bursts to maintain theoutput of the charge pump at about V3. If the controller 306 ceasesproviding the PWM signal bursts or delays too long before providing aburst, the charge pump will not output a voltage V3 sufficient to turnon the pilot switch 418. The pilot switch 418 will turn off (or stayoff), the pilot valve 314 will be closed, the pilot burner 41 will notreceive gas through the pilot valve 314, and the pilot burner 41 will beextinguished. A generally similar control procedure is used to hold openthe main valve 312 using the first main switch 412 and the main chargepump 416. The addition of the second main switch 414 and the pickcircuit 310 change the operation as described below.

The valve pick system 310 includes a pick switch 422 and a pick circuit424. The pick circuit 424, the pick switch 422, and both main valveswitches 412 and 414 are utilized for picking open the main valve 312.The controller 306 outputs the voltage V2 to the pick circuit 424 tocharge a pick circuit capacitor (not shown) to, ideally, the voltage V2.In reality, the pick circuit capacitor may be charged to a voltage thatis slightly less than V2. The pick circuit capacitor will take time tocharge. The controller 306 monitors the voltage of the pick capacitor.When the pick capacitor is charged to a voltage greater than a pickingthreshold voltage, the controller 306 may pick open the main valve 312.The picking threshold voltage is less than the voltage V2, but more thanthe minimum voltage needed to open the main valve 312. In one example,the minimum voltage needed to open the main valve 312 is between about1.7 volts and 2.0 volts, and the picking threshold voltage is about 3volts. In other embodiments, the picking threshold voltage is a voltagebetween about 1V and 5V. Alternatively, the picking threshold voltagemay be any voltage greater than the minimum voltage sufficient to openthe main valve 312. Thus, the output of the pick circuit 424 may be anyvoltage between about 3 volts and about 5 volts. To pick the main valve,the controller 306 sends a burst of PWM signals to the main charge pump416 to charge the charge pump 416 to a voltage V4 sufficient to turn onthe first main switch 412. In the example embodiment, the magnitude ofthe voltage V4 will vary with the varying of voltages V1 and V2. Forexample, when the voltage V2 is about 5 volts, the voltage V4 will beabout negative 2 volts. In another embodiment, the voltage V4 will beabout negative 3.15 volts. In other embodiments, the voltage V4 is anyother voltage suitable for turning on the first main switch 412. Thecontroller 306 periodically provides PWM signal bursts to maintain theoutput of the main charge pump 416 at about V4. If the controller 306ceases providing the PWM signal bursts or delays too long beforeproviding a burst, the main charge pump 416 will not output a voltage V4sufficient keep the first main switch 412 turned on. The second mainswitch 414 is initially off. After the first main switch 412 is turnedon, the controller 306 turns the pin connected to the pick switch 422 toa high output in order to activate the pick switch 422. The energystored in the pick circuit capacitor is coupled to the main valve 312through the pick switch 422 and the main valve 312 opens. The secondmain switch 414 is closed briefly before the pick switch 422 is opened.Closing the second main switch 414 couples the thermoelectric generator402 voltage V1 to the main valve 312 through the first and second mainswitches 412 and 414 to hold the main valve 312 open so the main burner30 remains lit. To keep the main burner 30 lit, the controller 306 keepsthe main switches 412 and 414 on by maintaining the output pin coupledto the second main switch 414 high and periodically sending bursts ofPWM signals to the main charge pump 416. To turn off the main burner 30,the controller 306 opens both main switches 412 and 414, therebyinterrupting the connection between the main valve 312 and thethermoelectric generator 402.

The second main switch 414 is used in both picking and holding open themain valve 312 and can be considered part of both the valve pick system310 and the valve control system 308. The second main switch 414 ensuresthat substantially all of the picking voltage is directed from the pickcircuit 424 to the main valve 312. The first main switch 412 and thesecond main switch 414 are MOSFETS with internal body diodes. The firstmain switch 412 has an internal body diode with its cathode pointedtoward the thermoelectric generator 402. The second main switch 414 hasits body diode with the cathode pointed toward the main valve 312 (andaway from the first main switch 412). Without the second main switch414, when the pick switch 422 is turned ON, the pick voltage wouldappear on the main valve 312 and simultaneously on the first main switch412. Even with the first main switch 412 turned off, the 3 to 5V pickspike may be sufficient to forward bias the internal body diode of firstmain switch 412, allowing current to flow through the first main switch412 to discharge through the thermoelectric generator 402 sourceresistance to ground. This could have an adverse effect on thethermoelectric generator 402 and it is a loss of power that could beused for picking the main valve 312. The second main switch 414,however, has its internal body diode oriented opposite of the first mainswitch 412. When the second main switch 414 is off, the pick voltagereverse biases the internal body diode of the second main switch 414,preventing the flow of current to the thermoelectric generator 402 andpermitting substantially all of the pick current to travel to the mainvalve 312. Alternatively, the second main switch 414 may be eliminatedand the first main switch 412 may be oriented as the second main switch414, i.e., with its internal body diode's cathode pointed toward themain valve 312 and its anode toward the thermoelectric generator 402. Insuch an embodiment, the first main switch's body diode will be reversebiased by the pick voltage and substantially all of the pick currenttravels to the main valve 312.

When it is determined that picking of the main valve 312 will occur, themain charge pump 416 is activated for 30 ms and first main switch 412 isturned on. The controller 306 will then go to sleep for 2 seconds toconserve power to let the voltage on the pick circuit capacitor rise.Upon waking at t=0 ms, the controller 306 turns on the pick switch 422.The pick circuit capacitor's voltage will begin decaying and currentbegins flowing through the main coil of the main valve 312. As thecurrent through the main coil increases the main valve 312 willeventually open. At a time between about t=20 ms and t=30 ms (dependingon the main valve's specific coils) the voltage from the pick circuitcapacitor is close to zero. The second main switch 414 is turned on tocouple the thermoelectric generator 402 output voltage to the main valve312 to hold the valve 312 open. At t=30 ms, the pick switch 422 isturned off. At t=30 ms to 60 ms, the controller provides a PWM burst tothe main charge pump 416 to keep the voltage V4 sufficient to keep thefirst main switch 412 turned on.

FIG. 6 is a circuit diagram of another embodiment of portion 600 of thevalve control system 308. The portion 600 may replace portion 500 (shownin FIG. 5D) of the valve control system 308. The portion 600 includesthe pilot hold switch 418, charge pump 420, and a discharge circuit 602.

The discharge circuit 602 is coupled to and controlled by the controller306. The controller 306 controls the discharge circuit 602 toselectively and quickly drain capacitor 604 to open pilot hold switch418. Thus, the controller can quickly open the pilot hold switch 418 toclose the pilot valve 314 with or without using the safety system 302.

The discharge system 602 is also used during switch checks of the system100. During normal operation, the controller 306 periodically checks thefunctionality of at least some of the switches of the system 306. Inparticular, the controller checks the functionality of the safety switch410, the pilot hold switch 418, and the first and second main switches412 and 414. The first and second main switches 412 and 414 are checkedfor functionality by reading a main monitor 502 (shown in FIG. 5C)during normal cycling of the main burner 30. To check the safety switch410 and the pilot hold switch 418, the conductive state of each switchis briefly (e.g., for about 1 ms) changed from its present state andinterrupter monitor 504 (shown in FIG. 5D) is read. When the safetyswitch 410 is ON or the pilot hold switch 418 is OFF, changing the stateof either switch removes the voltage over the coil in the pilot valve314. The magnetic field over the coil cannot, however, changeinstantaneously. If the switches 410 and 418 are returned to theiroriginal states before the magnetic field over the coil collapses, thepilot valve 314 will not close and the functionality may be testedwithout interrupting normal operation of the system 100. The dischargecircuit 602 allows the controller 306 to turn the pilot hold switch 418off quickly so that functionality may be checked without closing thepilot valve 314.

Embodiments of the methods and systems described herein achieve superiorresults compared to prior methods and systems. The dual main switchconfiguration limits or eliminates the flow of main valve pickingcurrent back to the thermoelectric generator without needing a largeresistor between the thermoelectric generator and the main valve. Thismay prevents potential adverse consequences of the revers current on thethermoelectric generator. Moreover, the dual main switch configurationsimplifies the timing for applying the valve picking current andapplying the main valve holding current. Furthermore, the example safetyswitch configuration allows the controller to shut down the power supplyto prevent the main valve and the pilot valve from being held open.Moreover, the safety switch configuration provides a different failuremode for the safety switch. For example, whether all switches of thecontrol system fail shorted or fail open, no voltage is applied to thecoils of the main and pilot valves.

Example embodiments of systems and methods for controlling a waterheater are described above in detail. The system is not limited to thespecific embodiments described herein, but rather, components of thesystem may be used independently and separately from other componentsdescribed herein. For example, the controller and processor describedherein may also be used in combination with other systems and methods,and are not limited to practice with only the system as describedherein.

When introducing elements of the present disclosure or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” “containing” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. The use of terms indicating a particular orientation (e.g.,“top”, “bottom”, “side”, etc.) is for convenience of description anddoes not require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing(s) shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A control system for controlling a gas poweredappliance including at least one electrically actuated gas valve forselectively providing gas to a burner, the control system comprising: apower source to provide electrical power to control the at least oneelectrically actuated gas valve; a valve control system configured toselectively couple electrical power from the power source to theelectrically actuated gas valve, the valve control system comprising: afirst switch having an on state to permit current to pass through thefirst switch and an off state to prevent current from passing throughthe first switch; and a second switch having an on state to permitcurrent to pass through the second switch and an off state to preventcurrent from passing through the second switch, the first switch and thesecond switch electrically connected in series between the power sourceand the electrically actuated gas valve; a controller operativelyconnected to the first switch and the second switch and configured tocontrol the first switch and the second switch to selectively couplepower from the power source to the electrically actuated gas valve; andwherein the first switch and the second switch each include a body diodehaving an anode and a cathode, and wherein first and second switches areconnected in series with their anodes connected together.
 2. The controlsystem of claim 1, wherein the first switch is operatively connected tothe power source with its body diode cathode operatively connected tothe power source, and the second switch is operatively connected to theelectrically actuated gas valve with its body diode cathode operativelyconnected to the electrically actuated gas valve.
 3. The control systemof claim 2, further comprising a valve picking system operativelyconnected to the electrically actuated gas valve at a location betweenthe valve control system and the electrically actuated gas valve, thevalve picking system configured to selectively couple a picking currentto the electrically actuated gas valve to open the gas valve.
 4. Thecontrol system of claim 3, wherein the picking current is not coupled tothe electrically actuated gas valve through the first switch or thesecond switch.
 5. The control system of claim 3, wherein the controlleris configured to turn on the first switch and turn off the second switchbefore the picking current is coupled to the electrically actuated gasvalve.
 6. The control system of claim 5, wherein the controller isconfigured to turn on the second switch after the picking current causesthe electrically actuated gas valve to open.
 7. The control system ofclaim 5, wherein the controller is configured to turn on the secondswitch a predetermined period of time after the picking current iscoupled to the electrically actuated gas valve.
 8. The control system ofclaim 3, further comprising a safety switch operatively connected to thecontroller and configured to selectively prevent the power system fromproviding sufficient power to the valve control system to hold theelectrically actuated gas valve open.
 9. The control system of claim 8,wherein a first terminal of the safety switch is operatively connectedto the first switch and the power system, and a second terminal of thesafety switch is operatively connected to a safety load.
 10. A waterheater comprising: a storage tank; a main burner configured to burn gasto heat water in the storage tank; a main gas valve coupled to the mainburner and having an open position permitting gas flow through the maingas valve and a closed position preventing gas flow through the main gasvalve, wherein the main gas valve is an electrically actuate gas valve;and a control system configured to control operation of the main burnerto provide water in the storage tank substantially at a setpointtemperature, the control system comprising: a power source to provideelectrical power; a valve control system configured to selectivelycouple electrical power from the power source to the main gas valve, thevalve control system comprising: a first switch having an on state topermit current to pass through the first switch and an off state toprevent current from passing through the first switch; and a secondswitch having an on state to permit current to pass through the secondswitch and an off state to prevent current from passing through thesecond switch, the first switch; and the second switch electricallyconnected in series between the power source and the main gas valve; acontroller operatively connected to the first switch and the secondswitch and configured to control the first switch and the second switchto selectively couple power from the power source to the main gas valve;and wherein the first switch and the second switch each include a bodydiode having an anode and a cathode, and wherein first and secondswitches are connected in series with their anodes connected together.11. The water heater of claim 10, wherein the first switch isoperatively connected to the power source with its body diode cathodeoperatively connected to the power source, and the second switch isoperatively connected to the main gas valve with its body diode cathodeoperatively connected to the main gas valve.
 12. The water heater ofclaim 11, wherein the control system further comprises a valve pickingsystem operatively connected to the main gas valve at a location betweenthe valve control system and the main gas valve, the valve pickingsystem configured to selectively couple a picking current to the maingas valve to open the main gas valve.
 13. The water heater of claim 12,wherein the picking current is not coupled to the main gas valve throughthe first switch or the second switch.
 14. The water heater of claim 12,wherein the controller is configured to turn on the first switch andturn off the second switch before the picking current is coupled to themain gas valve.
 15. The water heater of claim 14, wherein the controlleris configured to turn on the second switch after the picking currentcauses the main gas valve to open.
 16. The water heater of claim 14,wherein the controller is configured to turn on the second switch apredetermined period of time after the picking current is coupled to themain gas valve.
 17. The water heater of claim 12, further comprising asafety switch operatively connected to the controller and configured toselectively prevent the power system from providing sufficient power tothe valve control system to hold the main gas valve open.
 18. The waterheater of claim 17, wherein a first terminal of the safety switch isoperatively connected to the first switch and the power system, and asecond terminal of the safety switch is operatively connected to asafety load.